Bind Change Mechanism

Overview of Beta Change Mechanism💡

The 𝛃 subunit has 3 conformational states

O (Open): In this state, nucleotides and Pi can bind and be released
L (Loose): In this state, the molecules are trapped in the active site but are LOOSELY bound
T (Tight): In this state, the molecules are brought in such close proximity to each other that they undergo the reaction. → Make ATP

As a reminder, the 𝛃 subunit is interlocked with alpha subunits. These subunits do NOT move, and instead undergo these conformational changes when the gamma subunit turns and presents different sides to each subunit. Each beta subunit undergoes these conformational changes! So, say the flat portion of the gamma subunit (right side) turned clockwise to face a different subunit. This beta subunit would now be in the same conformational state as the previous. (Releasing ATP).

C-Ring Rotation:

The C-ring must rotate to make the ɣ subunit rotate in order to get the conformational changes in the Beta subunit as mentioned above.

Step 1: The proton binds

The H+ moves in through the ½ channel of the a subunit. From here, there are glutamate residues in the C ring that are negatively charged, which attracts the positive H+ ions, causing them to bind. This then neutralizes the negative charge on glutamate.

So what?

The glutamate is negatively charged and is therefore not able to interact with the lipid bilayer. When the proton binds, it IS able to interact since it is now neutral! (It will be able to spin into the membrane where before it was blocked),

Step 2: Rotation

Since it can now interact with the lipid bilayer, the protonated c subunit of the c ring (the specific subunit that was protonated) can rotate into the lipid bilayer.

This means it can only rotate ONE way (clockwise)

Step 3: Release

Finally, after enough protons bind, the H will reach the matrix facing a subunit. When this happens, the high pH (low amount of H+) will cause the H+ to jump off the c subunit.

Step 4: Cycle!

This cycle is perpetuated and allows the C ring to spin

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